Visa requirements, documentation and processing times vary by country, nationality and visa category, and they change. Check the current rules with the relevant consulate or your institution's international office rather than relying on a previous case.
You want a colleague from Vietnam at your conference. The scientific case is clear, the invitation is written, and you have some funds.
Between that point and the person standing in your seminar room there are several steps that are invisible from your side, and each of them stops the whole thing if it is missed.
The real cost
Budget for more than the flight. A realistic list:
International flight, usually with a connection. Accommodation for the conference days plus at least one extra night — long-haul arrivals rarely align with programme start times. Conference registration, which is often a significant sum on its own. Local transport. Meals not covered by the programme. Visa fee. And, depending on the destination, travel and health insurance that may be mandatory for the visa.
Two items commonly missed: the cost of getting to the international airport within Vietnam, which for someone outside Hanoi or Ho Chi Minh City means a domestic flight or a long journey; and the visa application appointment, which may itself require travel to a consulate.
Why reimbursement often does not work
This is the single most important point in this article.
Reimbursement means the traveller pays first and is repaid later. For many colleagues, the upfront amount is a substantial share of monthly income, and the delay before repayment can be months.
The result is not that they complain. The result is that they decline the invitation, usually with a polite reason that has nothing to do with money.
Three alternatives, in order of preference:
Book and pay directly — your institution buys the flight and the accommodation. Cleanest, and it removes the problem entirely.
Advance payment before travel.
Waive the registration fee — often within the organisers' gift and worth doing even when the rest is funded.
If your institution's rules genuinely only allow reimbursement, say so early and explicitly, so the invitee can decide with full information rather than discovering it after accepting.
The visa application: what it needs from you
The applicant assembles most of the file, but several documents can only come from the host, and delays here are usually the host's fault rather than the applicant's.
Typically needed:
A formal invitation letter on institutional letterhead, signed, naming the event, the dates, the applicant's role, and — importantly — who is paying for what. A letter that does not state the financial arrangement is much weaker.
Proof of the funding — a letter confirming the costs are covered, or the actual bookings.
Conference documentation — the programme showing the person's name, or the acceptance notice.
Sometimes a supporting letter from your institution's international office. Find out early whether this exists at your institution and how long it takes.
Send these as early as possible and send them together. An applicant who has to come back three times for missing documents loses days at each step.
Timing
Work backwards from the conference date:
Four to six months before: the invitation and the funding decision.
Three months before: all documents in the applicant's hands.
Two to three months before: the visa appointment — appointment slots themselves can be weeks out, which is the step most often underestimated.
Six weeks before: bookings confirmed.
An invitation issued eight weeks before the event is, for most destinations, an invitation that cannot be accepted. If that is your timeline, say so and ask whether it is feasible rather than assuming it is.
If the visa is refused
It happens, and often for reasons the applicant cannot control or even learn.
Three things worth having ready:
A remote presentation option, arranged in advance rather than improvised the night before.
A cancellable booking policy, so a refusal does not also cost the person money.
A willingness to write again for a later occasion. A refusal is not evidence about the person, and treating it as such — quietly dropping them from future invitations — is a real and common injustice.
Making the trip worth the cost
A long journey for a twenty-minute talk is a poor use of everyone's resources. Four additions that cost little:
A seminar in your department, separate from the conference session.
Scheduled meetings with two or three specific people — arranged in advance, not left to chance in the coffee break.
A visit to a facility relevant to their work.
An explicit conversation about what could come next — a joint proposal, an exchange, a co-supervision. The trip is the occasion; the collaboration is the point, and it rarely forms by itself.
What costs are commonly missed?
Travel to the international airport within Vietnam, which for someone outside the two largest cities means a domestic flight; and travel to a consulate for the visa appointment.
Why is reimbursement a problem?
The upfront amount can be a substantial share of monthly income and repayment may take months — so the invitation is usually declined for an unrelated-sounding reason.
What must the invitation letter state?
The event, dates, the person's role, and explicitly who is paying for what — a letter without the financial arrangement is much weaker.
How early should an invitation be issued?
Four to six months before, since visa appointment slots alone can be weeks out; an invitation eight weeks before often cannot be accepted.
